Abstract
The relation between the Hubble constant and the scale of supersymmetry breaking is investigated in models of inflation dominated by a string modulus. Usually in this kind of model the gravitino mass is of the same order of magnitude as the Hubble constant, which is not desirable from the phenomenological point of view. It is shown that slow-roll saddle point inflation may be compatible with a low scale of supersymmetry breaking only if some corrections to the lowest-order Kähler potential are taken into account. However, choosing an appropriate Kähler potential is not enough. There are also conditions for the superpotential and, for example, the popular racetrack superpotential turns out to be not suitable. A model is proposed in which slow-roll inflation and a light gravitino are compatible. It is based on a superpotential with a triple gaugino condensation and the Kähler potential with the leading string corrections. The problem of fine-tuning and experimental constraints are discussed for that model.